<template>
  <scroll class="listview"
          :data="data"
          ref="listview"
          :listenScroll="listenScroll"
          :probeType = "probeType"
          @scroll="scroll"
  >
    <ul>
      <li v-for="group in data" class="list-group" ref="listGroup">
        <h2 class="list-group-title">{{group.title}}</h2>
        <ul>
          <li @click="selectItem(item)" v-for="item in group.items" class="list-group-item">
            <img v-lazy="item.avatar" class="avatar">
            <span class="name">{{item.name}}</span>
          </li>
        </ul>

      </li>
    </ul>
    <div class="list-shortcut" @touchstart="onShortcutTouchStart" @touchmove.stop.prevent="onShortcutTouchMove">
      <ul>
        <li v-for="(item,index) in shortcutList"
            class="item" :data-index="index"
            :class="{'current':currentIndex===index}"

        >
          {{item}}
        </li>

      </ul>
    </div>
    <div class="list-fixed" v-show="fixedTitle" ref="fixed">
      <h1 class="fixed-title">{{fixedTitle}}</h1>
    </div>

    <div v-show="!data.length" class="loading-container">
      <loading></loading>
    </div>
  </scroll>

</template>

<script type="text/ecmascript-6">
  import Scroll from 'base/scroll/scroll'
  import {getData} from "common/js/dom";
  import index from "../../router";
  import Loading from 'base/loading/loading'

  const ANCHOR_HEIGHT = 18
  const TITLE_HEIGHT=30

  export default {
    created() {
      this.touch = {} // 数据共享
      this.listenScroll = true
      this.listHeight = []
      this.probeType=3
    },
    data() {
      return {
        scrollY: -1,
        currentIndex: 0,
        diff: -1
      }
    },
    name: "listview",
    props: {
      data: {
        type: Array,
        default: []
      }

    },
    computed: {
      shortcutList() {
        return this.data.map((group) => {
          return group.title.substr(0, 1)
        })
      },
      fixedTitle(){
        if (this.scrollY>0){
          return ""
        }
        return this.data[this.currentIndex]? this.data[this.currentIndex].title:""
      }
    },

    methods: {
      refresh(){
        this.$refs.listview.refresh()
      },
      selectItem(item){
        this.$emit('select',item)
      },

      onShortcutTouchStart(e) {
        let anchorIndex = getData(e.target, 'index')
        let firstTouch = e.touches[0]
        this.touch.y1 = firstTouch.pageY
        this.touch.anchorIndex = anchorIndex // 将index值提取为公共参数
        this._scrollTo(anchorIndex)
      },
      onShortcutTouchMove(e) {
        let firstTouch = e.touches[0]
        this.touch.y2 = firstTouch.pageY
        let delta = (this.touch.y2 - this.touch.y1) / ANCHOR_HEIGHT | 0// 获取y轴上的偏移量 然后比上元素的高度取得整数
        // console.log("delta : "+delta);
        let anchorIndex = parseInt(this.touch.anchorIndex) + delta // 在index基础下增加偏移量
        //console.log("anchorIndex : "+anchorIndex);
        this._scrollTo(anchorIndex)

      },
      scroll(pos) {
        this.scrollY = pos.y // 实时获取BatterScroll 滚动的y轴的距离
       // console.log("this.scrollY : "+this.scrollY);
      },

      _scrollTo(index) {
       // console.log(index);
        if (!index&&index!==0){
            return
        }
        if (index<0){
          index =0
        } else if (index>this.listHeight.length-2){
          index = this.listHeight.length-2
        }

        this.scrollY = - this.listHeight[index]
        this.$refs.listview.scrollToElement(this.$refs.listGroup[index], 0)

      },
      _calculateHeight(){
        this.listHeight = []
        const list = this.$refs.listGroup
        let height = 0
        this.listHeight.push(height)
        for(let i =0;i<list.length;i++){
          let item = list[i] // 获取到每个Group 的元素
          height+=item.clientHeight
          this.listHeight.push(height)


        }

      },


    },
    watch:{
      data(){
        setTimeout(()=>{
          this._calculateHeight()
        },20)
      },
      scrollY(newY){ // 监听scrollY 值的变化
       // console.log("newY : "+newY);
        const listHeight = this.listHeight

        //当滚动到顶部, newY>0
        if (newY>0){
          this.currentIndex=0
          return
        }

        // 在中间部分滚动
        for (let i =0;i<listHeight.length-1;i++){

          let height1 = listHeight[i]
          let height2 = listHeight[i+1]
          //console.log("newY: "+newY+" height1: "+height1+" height2: "+height2)
          if ((-newY>=height1&&-newY<height2)){
            this.currentIndex = i
            this.diff = height2+newY
          //  console.log("currentIndex: "+this.currentIndex);
            return
          }
          //console.log("i: "+i);

        }
        // 当滚动到底部, 且-newY大于最后一个元素的上限  -2 是因为原本只有23条数据但是初始化了24个节点,并且index是从0 开始计算
        this.currentIndex=listHeight.length-2

        // console.log(this.currentIndex);


      },
      diff(newVal){ // 当间距变化的时候
        // 当间距大于0 并且小于模块本身时
        let fixedTop = (newVal>0&& newVal<TITLE_HEIGHT)?newVal-TITLE_HEIGHT:0
       // console.log("this.fixedTop: "+this.fixedTop);
        if (this.fixedTop===fixedTop){
         // console.log("this.fixedTop: "+this.fixedTop);
          return
        }
        this.fixedTop = fixedTop
        this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`
        //this.test="test"
      }
    },

    components: {
      Scroll,
      Loading
    }

  }
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
  @import "~common/stylus/variable"

  .listview
    position: relative
    width: 100%
    height: 100%
    overflow: hidden
    background: $color-background
    .list-group
      padding-bottom: 30px
      .list-group-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
      .list-group-item
        display: flex
        align-items: center
        padding: 20px 0 0 30px
        .avatar
          width: 50px
          height: 50px
          border-radius: 50%
        .name
          margin-left: 20px
          color: $color-text-l
          font-size: $font-size-medium
    .list-shortcut
      position: absolute
      z-index: 30
      right: 0
      top: 50%
      transform: translateY(-50%)
      width: 20px
      padding: 20px 0
      border-radius: 10px
      text-align: center
      background: $color-background-d
      font-family: Helvetica
      .item
        padding: 3px
        line-height: 1
        color: $color-text-l
        font-size: $font-size-small
        &.current
          color: $color-theme
    .list-fixed
      position: absolute
      top: 0
      left: 0
      width: 100%
      .fixed-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
    .loading-container
      position: absolute
      width: 100%
      top: 50%
      transform: translateY(-50%)
</style>
